rfc:number_format_separator
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rfc:number_format_separator [2015/12/23 00:09] – Slight restructure (partial rewrite #2) tpunt | rfc:number_format_separator [2017/09/22 13:28] (current) – external edit 127.0.0.1 | ||
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* Date: 2015-12-19 | * Date: 2015-12-19 | ||
* Author: Thomas Punt, tpunt@php.net | * Author: Thomas Punt, tpunt@php.net | ||
- | * Status: | + | * Status: |
* First Published at: http:// | * First Published at: http:// | ||
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Long numerical literals can be a source of poor readability in code. Take the following examples: | Long numerical literals can be a source of poor readability in code. Take the following examples: | ||
<code php> | <code php> | ||
- | 197823459; | + | // what number is this? |
- | 97802345932 > 97802349532; // which number is greater? | + | 197823459; |
- | 9803458239 === 9803457239; // are these numbers equal? | + | |
+ | // which number is greater? | ||
+ | 97802345932 > 97802349532; | ||
+ | |||
+ | // are these numbers equal? | ||
+ | 9803458239 === 9803457239; | ||
</ | </ | ||
- | These are difficult to read and difficult reason about. To ameliorate this issue, this RFC proposes the introduction of a digit separator in numerical literals. This will enable | + | These are difficult to read and difficult reason about. To ameliorate this issue, this RFC proposes the introduction of a digit separator in numerical literals. This will enable the examples |
<code php> | <code php> | ||
- | 197_823_459; | + | // what number is this? |
- | 97_802_345_932 > 97_802_349_532; // which number is greater? | + | 197_823_459; |
- | 9_803_458_239 === 9_803_457_239; // are these numbers equal? | + | |
+ | // which number is greater? | ||
+ | 97_802_345_932 > 97_802_349_532; | ||
+ | |||
+ | // are these numbers equal? | ||
+ | 9_803_458_239 === 9_803_457_239; | ||
</ | </ | ||
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0b0010_1101; | 0b0010_1101; | ||
0267_3432; // versus 02673432 | 0267_3432; // versus 02673432 | ||
+ | 1_123.456_7e2 // versus 1123.4567e2 | ||
</ | </ | ||
- | ==== Chosen | + | The underscores will be stripped out during the lexing stage, and so the runtime will not be affected in any way. For example: |
+ | <code php> | ||
+ | var_dump(1_000_000); | ||
+ | </ | ||
+ | |||
+ | ==== Chosen | ||
+ | |||
+ | The digit separator is used to mark boundaries between digits - it is not used to separate digits from other characters. The following syntax choices are therefore based on this. | ||
- | === Disallow | + | === Disallow |
Leading underscores will not enhance readability and will conflict with constant naming conventions. | Leading underscores will not enhance readability and will conflict with constant naming conventions. | ||
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</ | </ | ||
- | === Disallow | + | === Disallow |
- | Trailing underscores will not enhance readability | + | Trailing underscores will not enhance readability |
<code php> | <code php> | ||
- | 100_; // PHP Parse error: | + | 100_< |
</ | </ | ||
- | === Disallow | + | === Disallow |
Allowing for two or more underscores to be placed together will provide no further readability benefits. | Allowing for two or more underscores to be placed together will provide no further readability benefits. | ||
<code php> | <code php> | ||
- | 1__000; // PHP Parse error: | + | 1__000___000_000; // Parse error: syntax error, unexpected '__000___000_000' (T_STRING)... |
</ | </ | ||
- | === Enable | + | === Enable |
- | Underscores are not allowed around the period for floats, around the **0x** for hexadecimal | + | Underscores are not allowed around the period for floats, around the **0x** for hexadecimal |
<code php> | <code php> | ||
- | 100_.0; // PHP Parse error: | + | 100_.0; // Parse error: |
- | 100._01; // PHP Parse error: | + | 100._01; // Parse error: |
- | 0x_0123; // PHP Parse error: | + | 0x_0123; // Parse error: |
- | 0b_0101; // PHP Parse error: | + | 0b_0101; // Parse error: |
+ | 1_e2; // Parse error: syntax error, unexpected ' | ||
+ | 1e_2; // Parse error: syntax error, unexpected ' | ||
+ | </ | ||
- | 100_000; // interpreted as 100000 | + | === Enable for arbitrary grouping of digits === |
- | 10_0.0_112; // interpreted | + | |
- | 0b01_10_11_00; // interpreted | + | Underscores may be freely interspersed between arbitrary groups of digits, enabling for developers to group the digits as they see fit. One such argument for relaxing the interspersing of underscores is that not all countries group digits in sets of three [1]. |
+ | <code php> | ||
+ | 1_234_567; // grouped in sets of 3 | ||
+ | 123_4567; // grouped in sets of 4 (Japan, China) | ||
+ | 1_00_00_00_000; | ||
+ | |||
+ | 0x11_22_33_44_55_66; | ||
+ | 0x1122_3344_5566; // a number to be used as 16-bit data, grouped by word | ||
</ | </ | ||
- | ==== Why the Underscore Character? ==== | + | ==== Why the underscore character? ==== |
- | The underscore | + | |
+ | The underscore: | ||
+ | * Is easy to type on the majority | ||
+ | * Does not conflict with PHP's grammar | ||
+ | * Acts as a clear and unambiguous delineator between digits (unlike the comma or period) | ||
- | The following | + | It has also been widely adopted as a digit separator in a number of other languages, including: |
* Ada | * Ada | ||
* D | * D | ||
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* Elixir | * Elixir | ||
- | Few other languages have deviated from using the underscore to separate digits. One notable | + | Few other languages have deviated from using the underscore to separate digits. One notable |
- | ==== Why no Support | + | ==== Why no support |
- | This RFC does not include stringy numerics because of the BC breakage involved. It will cause the coercion rules for strings to integers | + | This RFC does not include stringy numerics because of the BC breakage involved. It would mean changing |
+ | |||
+ | If formatting stringy | ||
===== Backward Incompatible Changes ===== | ===== Backward Incompatible Changes ===== | ||
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Support for stringy numerics could be added in the next major version. | Support for stringy numerics could be added in the next major version. | ||
- | ===== Proposed Voting Choices | + | ===== Vote ===== |
- | A simple yes/no voting option | + | A simple yes/no voting option |
+ | |||
+ | <doodle title=" | ||
+ | * Yes | ||
+ | * No | ||
+ | </ | ||
+ | |||
+ | Voting starts on January 13th and ends on January 20th. | ||
===== Patches and Tests ===== | ===== Patches and Tests ===== | ||
- | A patch has been made - this part will be updated soon. | + | PR: https:// |
===== Implementation ===== | ===== Implementation ===== | ||
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===== References ===== | ===== References ===== | ||
+ | Current discussion: https:// | ||
+ | |||
Previous discussion on separators for numerical literals: https:// | Previous discussion on separators for numerical literals: https:// | ||
- | Current discussion: to be updated... | + | |
+ | [1]: http:// | ||
===== Rejected Features ===== | ===== Rejected Features ===== | ||
Keep this updated with features that were discussed on the mail lists. | Keep this updated with features that were discussed on the mail lists. |
rfc/number_format_separator.1450829356.txt.gz · Last modified: 2017/09/22 13:28 (external edit)